1. Field of the Invention
The present invention relates to a method for interpreting data used for clinical diagnostic purposes. In particular, a decision tree is disclosed for interpreting tandem mass spectrometry data relating to the quantification of metabolites used for diagnosing newborn babies.
2. Description of the Related Art
Automated methods for assessing a patient""s condition are known. Computerized systems can be integrated to produce data that can be compared to a known result to allow for proper diagnosing. Such data might be produced by a MRI or CAT scanner, which is used to identify components within the human body.
One particular instrument used for identifying components of interest, whether they are of medicinal or chemical interest, is the mass spectrometer. In reference to U.S. Pat. No. 5,453,613, compounds, when introduced to the electrospray tandem mass spectrometer, are ionized and essentially fragmented. Each fragment produces a peak having local maximums that are matched to reference spectra. A compound can be identified by its associated fragments, each having a mass to charge ratio, which is then relative to the concentrations-of each fragment. All of the reference spectra and compound names can then be stored in a library for correlation and determination. Thus, mass/charge ratios can be used to identify components from known spectra stored in a database.
More recently, however, the use of spectrometry has been implemented in the field of clinical diagnosis. See Chace, U.S. application Ser. No. 09/277,119.
Inborn errors of metabolism usually result from defective enzymes or cofactors. Resulting genetic disorders can be diagnosed by the metabolic profiling of amino acids and acylcarnitines taken from blood spots subjected to a sampling protocol and thereafter introduced into an electrospray tandem mass spectrometer. An electrospray tandem mass spectrometer is very sensitive and specific and can detect a broad spectrum of disorders at the genetic level. With proper standards, data produced from the spectrometer includes values for particular metabolites. The metabolites that are of interest in detecting these disorders are, in particular, amino acids and acylcarnitines/carnitines and the derivatives thereof.
The spectra and resulting concentration values of each metabolite, as derived from mass spectrometry, are then compared to thresholds as a means for evaluating the contents of the blood sample. These thresholds determine the appropriate course of action necessary as a follow-up to the spectral analysis.
As seen in Wright et al., U.S. Pat. No. 5,545,895, spectrometry data is applied to a computerized search database for matching each component as a means of identification. In a clinical diagnostic setting, there must be further methods for evaluation beyond just that of the identification itself. The numbers must be quantified. Newborns can be born with metabolic disorders, which, if not treated within days, can result in death. Thus, after obtaining MS/MS (tandem mass spectrometer) data from blood samples from newborns, generally of the age of less than seven days old, there is a need for efficiently interpreting this data in relation to pre-determined metabolite concentration thresholds. This interpretation allows for proper decision-making necessary for the diagnosing and follow-up testing of newborns.
The objective of the present invention is to provide a method for interpreting electrospray tandem mass spectrometry data from the steps following analysis to diagnosis. The method provides the next course of action necessary in determining the deficiency or elevation of a particular fragment directly proportional to a concentration of a metabolite that may cause a genetic defect. In accordance with U.S. application Ser. No. 09/277,119, when an abnormal sample is flagged after being scanned, a recommended action is to be taken. The present method is a guideline for the necessary action following the preliminary analysis.
Internal standards are used to provide the quantitative information needed to detect specific components. Use of proper ratios of respective ions enables the detection of many metabolites at one time. Each particular metabolite is produced as a fragment yielding a concentration within the spectrometer after being quantified and derivatized from a blood spot. Each metabolite concentration is compared to a flag concentration, which is a quality assurance indicator used to identify a proper sampling quantification and analysis, and which is a diagnostic limit in determining whether or not the concentration of the metabolite is significant. The flag is pre-determined based on a standard deviation from what a normal concentration of a particular metabolite should be. This concentration threshold, or flag, must be appropriated for each scan done and for each type of metabolite reviewed. The concentration values produced will be above or below this threshold flag, which allows for the determination of the next course of action, whether it be a re-analysis or the interpretation that the baby is normal.
As an example, medium chain acyl-CoA dehydrogenase (MCAD) deficiency could be a result of an increased concentration of octanoylcarnitine (Chace et al.). Deficiency in the activity of MCAD presents with a Reye-like syndrome, mild hypoglycemia, or sudden death. The present method provides for numerical guidelines for determining just how significant the elevation is at the time of birth, and what the next step in the screening process would be, such as a follow-up and confirmatory DNA test. In this manner, decision trees for interpreting the concentrations for amino acids and acylcarnitine/carnitines are presented, some of which, if properly diagnosed, can lead to treatment. Each of these potentially fatal blood elevations or deficiencies is compared against the quantified concentration thresholds to allow for immediate attention and action. The comparison with the threshold flags also is a determining factor for maintaining instrument quality and accuracy. This decision making process, coupled with the current method of screening newborns using electrospray tandem MS/MS, allows for a complete protocol for analyzing and diagnosing newborns with genetic disorders.